Wierd Problem with Propeller Moving to EEPROM Starup

GeofPrice

I have a Propeller program that works perfectly as long as I am running off of RAM, or if I load the program to EEPROM and keep the USB plugged in. I can power down the propeller circuitry, then power back up and the propeller starts up fine, as long as the USB is connected. I have tested this pretty thoroughly. I can close the propeller tool program, power down the propeller chip, unplug the USB, plug it back in, and the program starts fine off the EEPROM. If I do exactly the same thing with the USB disconnected, the EEPROM won't start. I changed the crystal and tried 1/2 crystal speed and 1/2 multiplier so it is running 20 MHz instead of 80 MHz. No luck. Needs to have the USB connected for it to work. Any help someone can give? I have a Propstick which has all the crystal and USB connected on the miniature circuit board.

Mike Green

The only thing that makes sense of this is a problem that occurs when the FTDI chip is unpowered (from USB) and the Propeller program tries to transmit data to it. The Propeller's transmit pin acts as a source of power for the FTDI chip, but not enough for proper operation, just enough to cause a reset.

One solution is to check the state of the receive pin. If it's low, there's probably no USB connection and the FTDI chip is not powered. Your program skips any initialization of the USB serial port and skips any usage of the port.

Another solution is to just not use the USB serial port in your program.

There are some hardware changes you can make to always provide power to the FTDI chip, even if there's no USB power source, but the above software changes are easier.

GeofPrice

Thanks, Mike. I had multiple USB transmits for debugging purposes, and since I didn't need them anymore, I removed them and everything works!

Rayman

Sounds like the FTDI reset bug strikes again! If we had a troubleshooting guide, I think this should be one of the first things mentioned...